Depending on the angle, the amplifier can be divided into different categories. The amplifier can be divided into A, B, C, D, and AB according to the signal conduction angle. We will introduce them one by one in this article.
Class A amplifierA pure class A amplifier, the final stage amplifier, operates in a Class A amplifier, also known as a pure Class A amplifier. Class A amplifiers have current flowing through the transistor (ie, the conduction angle is 3600) over the entire period of the input signal. This type of amplifier is called a Class A amplifier. Class A amplifiers have very low distortion, but their efficiency is low. Even in the ideal case, the maximum efficiency can only reach 50%. Usually only 30%~40%0 has current flowing through the transistor in the half cycle of the input signal. (ie, the conduction angle is 1800), this amplifier is called a class B amplifier. Since the conduction angle is 1800, the other half of the input signal waveform is clipped off, so the distortion is large.
Two (or two) of the output stages of a Class A power amplifier (Class A power amplifier) ​​are always in a conducting state, that is, they maintain conduction current regardless of the presence or absence of a signal input, and make these two currents equal to the peak value of the AC. When the communication flows to the load under the maximum signal. When there is no signal, the two transistors each circulate an equal amount of current, so there is no unbalanced current or voltage at the output center point, so no current is input to the speaker. When the signal goes to the positive side, the output transistor above the line allows more current to flow in, and the lower output transistor reduces the current relatively. As the current begins to unbalance, it flows into the speaker and pushes the speaker to sound. Simply put, a pure class A amplifier always works at its maximum output power state.
Class B amplifierDue to the presence of the transistor's initial turn-on voltage value and the non-linearity of the initial turn-on, Class B amplifiers have crossover distortion, which is clearly not allowed in the high quality HI-FI amplification field. Therefore, the two transistors of the push-pull circuit are often biased to have a conduction angle slightly larger than 1800, which avoids crossover distortion. In this kind of circuit, the conduction angle is between Class A and Class B. The efficiency of the class AB class of the Class AB (Class A) amplifier is lower than that of Class B, only 60%~70%. However, because it takes into account the advantages of Class A and Class B (low distortion, high efficiency), it has been widely used.
Class AB amplifierClass A and Class B amplifiers are amplifiers that operate in Class A and Class B amplifiers. Also called class AB amplifier. Class AB belongs to the traditional power amplifier. It is also the type of most power amplifiers. From the power point of view, the power value of Class A and Class B is generally larger. But it doesn't always work at the maximum output power. Although the amplification type is not as good as the pure A class, the Class A amplifier can make a beautiful and exciting sound with a high level of debugging and tuning. Numerous HIFI vendors have proven this with facts.
Class C amplifierWhen the input signal exceeds the bias point, current flows through the transistor (ie, the conduction angle is less than 1800). This type of amplifier is called Class C (Class C) amplifier. Class C amplifier is more efficient, but its current waveform is too distorted. It is large and therefore cannot be used for Hi-Fi amplification. It can only be used for resonant power amplification using a high-Q tuning loop as a load. Since the tuning loop has filtering capability, the loop current and voltage are still close to a sinusoidal waveform with little distortion.
Class D amplifierClass D amplifiers refer to Class D audio power amplifiers (sometimes referred to as digital power amplifiers). By controlling the ON/OFF of the switching unit, the amplifier that drives the speaker is called a Class D amplifier. Class D amplifiers were first proposed in 1958 and have become popular in recent years. Compared with general linear class AB power amplifier circuits, class D power amplifiers are characterized by high efficiency and small size.
From the characteristics of the A, B, and C amplifiers, the main reason that affects the efficiency of the amplifier is the DC power consumption when there is no signal. The Class D (Class J) amplifier operating in the pulse amplification state has a working state of switching amplification, and the efficiency is extremely high, theoretically up to 100%. In fact, since the device does not reach the ideal state, the efficiency can only reach 80%. 95%, but this is also the highest efficiency in the amplifier. Due to the high efficiency of the class D power amplifier and the small reactive power loss, the heat sink volume can also be used less, and the transformer is not required to be so large, so that the volume, weight and cost of the power amplifier are greatly reduced, which is in line with people's high-performance power amplifier. The pursuit of efficiency and light weight.
Class D amplifiers are different from Class A and Class AB amplifiers. The latter receives an analog signal for amplification, the former is not necessarily. There are several different approaches to technology. There is a full digital digital "full digital amplifier" (only digital input terminals, no analog input), but also a half-digit digital "semi-digital amplifier." (with analog input terminal)
Class D power amplifiers are an amplification mode in which the amplifying element is in the operating state of the switch. When there is no signal input, the amplifier is in the off state and does not consume power. In operation, the transistor is brought into saturation by the input signal, and the transistor is equivalent to an on-switch, which directly connects the power supply to the load. An ideal transistor does not consume power because it has no saturation voltage drop. In fact, the transistor always has a small saturation voltage drop and consumes some of the power. This power consumption is only related to the transistor characteristics, and is independent of the magnitude of the signal output, so it is particularly advantageous for ultra-high power applications.
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